Smart Controller For Explosion-Proof Heaters

Intertec's
explosion-proof smart programmable controller is for precision temperature
regulation of process instrumentation and analyzer enclosures in hazardous
environments. The controller has a switching capacity of up to 10 A, enabling
it to be used with explosion-proof heaters with power ratings as high as
2,300W, depending on the ambient and required enclosure/equipment temperatures
and the heater supply voltage.

Heater systems based on Smart Controller 2.0 may
be used to control the temperature of equipment or the surrounding air in an
enclosure or cabinet, and are for use with analytical instruments that need to
be maintained at high temperatures and are located in hazardous environments.
Typical applications include analyzers handling difficult media in oil, gas and
petrochemical processing plants.

Intertec's range of THERM HI explosion-proof
electric heaters includes both finned and block styles, for convection air
heating or direct equipment heating by conduction, and covers output power
levels from 60 to 500W. They are available with a choice of 120 or 230V input,
and are also CSA C/US approved for 277 V.

The new digital PID
(proportional-integral-derivative) controller operates as a remote terminal
unit (RTU), and uses the Modbus RTU communications protocol over an RS485
serial network to facilitate easy integration with existing process control
systems. As many as 31 controllers can be set up and monitored in one branch of
a network.

Intertec's suite of PC software and LabView VI
drivers enable attributes to be programmed, including the controller's P and I
terms, a user-defined ramp for temperature increase against time and the
heater's temperature limit. The software has a data logging function for a
graphical record of temperature values retrieved over time from each
controller.

Additional facilities allow the controller to be
used as a temperature monitor, to provide a digital output when the temperature
is within a user-defined range; this could be used to control a cooling fan for
example.

Housed in an aluminum enclosure, the smart
controller has an IP66 protection rating and external surfaces have a saltwater
resistant finish. The PID controller and associated electronics are
encapsulated in silicone, with the Ex e electrical terminals accessible in a
separate compartment. Power to the heater element is handled by a proportional,
triac-based control circuit, which uses zero-voltage switching to minimize
electromagnetic interference.

There are two versions of controller: the
standard version features a compact housing measuring 57 x 125 x 80 mm (2.2 x 5
x 3.1 inches) and is suitable for IEC-Ex and ATEX Zone 1, 2 , 21 and 22 . When
installed in a NEMA 4X rated enclosure, the system is also approved for use in
North American hazardous environments rated Zone 1 or 2, Group IIC or Class I
or II, Division 2, Group A, B, C and D. The second version, developed for the
North American market, is designed to form part of a cable conduit system, and
is approved for Class I, Division 1 rated hazardous environments.

The smart controller incorporates three
temperature sensors; one is integrated in the controller housing, for measuring
local cabinet temperature, and another is embedded in the heater itself,
together with a temperature-sensitive fuse, to ensure that its surface
temperature can never exceed the specified 'T' rating. Intertec heaters are
available for T3, T4 and T6 temperature classes, limiting heater surfaces to
150, 90 or 50C respectively. The third is an intrinsically safe KTY silicon
temperature sensor mounted at the end of a cable, which can be freely
positioned in the instrument enclosure or embedded in the equipment that has to
be kept at a constant temperature. The standard version of the controller
features a built-in bi-color LED indicator which provides a useful local
diagnostic aid by showing any deviation from the set point temperature and
highlighting the occurrence of any heater error.

Intertec can supply the smart controller and the
customer's chosen heater as a complete package. The controller is delivered
ready to install, adapted to the heater, and pre-programmed with requested
parameter default values, including temperature set point, heating temperature
class, RS485 address and line voltage and frequency. In addition to the
PC-based software, an optional USB to RS485 interface converter is also
available.

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